27th Feb 2018

The legal implications of Japanese Knotweed in a neighbour's garden

Disputes between neighbours are a common occurrence, can arise for many reasons and can permanently sour relations between previously amicable neighbours. 

A recent County Court Case has highlighted one of the many areas a neighbour dispute can arise in – this one being a particularly knotty dispute relating to a legal battle between warring neighbours over Japanese Knotweed.

What is Japanese Knotweed?

Japanese Knotweed was brought to the United Kingdom in the 19th century after the plant was discovered in Japan growing on the side of volcanoes. Initially valued for its beauty, opinion changed when it was discovered the extensive and fast-growing roots can have catastrophic consequences on a building’s drains and foundations.

Japanese Knotweed can grow up to 10 cm a day between April and October. The roots can extend to a depth of three metres and up to seven metres laterally. If even a small piece of root is left in the ground, it can quickly re-infest the land.

Why can Japanese Knotweed be problematic?

The hostile plant can cause a range of headaches for landowners, including:

  • Physical damage to buildings and land. This can affect the value of the property, as well as its marketability and insurability;
  • The expense and time required to eradicate, often requiring specialist help to treat the plant;
  • The government has estimated the costs of eradicating all Japanese Knotweed from the UK is £2.6 billion;
  • Harm biodiversity by outcompeting other species of plants and animals; and
  • Criminal and civil liabilities for owners, occupiers and any person dealing with knotweed who fail to do so in accordance with the law.
What liability does an owner have?

An owner or occupier of land is not obliged to control, remove or treat Japanese knotweed on their land. They can be liable, however, should they allow the knotweed to spread onto neighbouring land. The neighbour could then issue private nuisance proceedings in the Civil Courts for:

  • damages for loss of enjoyment and diminution of value;
  • the costs of removal; and
  • an injunction against re-infestation.

As the case of Adam Smith and Eleanor Smith v Rosemary Line demonstrates there is also a significant risk that even if the knotweed does not spread onto the neighbour’s land, the owner may still be liable to the diminution in value of the neighbour’s land for the knotweed simply being in the vicinity.

Even if the knotweed does not spread, there may still be liability for the diminution in value of the neighbour’s land for the knotweed simply being in the vicinity.

In addition, Local Authorities have the power to serve notice on an occupier of land containing knotweed. This notice can require them, within a set period, to remedy any knotweed which could adversely affect the amenity of an area. Failure to abide by this or to properly dispose of the knotweed (such as discarding it in the wild) can lead to criminal liabilities.


Any owner or occupier dealing with Japanese knotweed would be well advised to seek specialist help.

The case of Adam Smith and Eleanor Smith v Rosemary Line

The claimants, (Mr and Mrs Smith) purchased a seaside property 15 years ago. At the time they were unaware that destructive Japanese Knotweed was growing on a neighbouring property owned by the defendant (Ms Line).

What followed was a 15-year dispute between the neighbours as the knotweed grew closer to the claimant’s land. When it became apparent to the Smiths that Ms Line was not going to take the steps they required to remove the knotweed, they issued court proceedings.

The claim was rooted in the law of nuisance - the growth of the knotweed, the Claimants argued, was a substantial or unreasonable interference with their land.

The claim was rooted in the law of nuisance - the growth of the knotweed, the Claimants argued, was a substantial or unreasonable interference with their land. This interference was caused by a feature of the defendant’s land, the knotweed that she was allegedly failing to control. The claimants asserted their loss was caused by the presence of the weed which could knock 10% (£50,000) off the value of the beach-side family home.

Ms Line’s line of defence was that she had done everything possible to stop the spread through maintenance and herbicides. 

The case went before a Judge in October last year, with the ruling being published this month.

The court ruled in favour of the claimants. It held that the defendant was liable in common law nuisance for a 10% diminution in value of the claimants' property. Ms Line was ordered to employ a contractor over the next five years to eradicate the weed, as well as pay substantial legal costs, believed to run into tens of thousands of pounds.

The court that the defendant was liable in common law nuisance for a 10% diminution in value of the claimants' property

The decision follows a similar case in 2017 (Williams v Network Rail Infrastructure Ltd [2017]).

This case involved a group of homeowners in Wales who took action against Network Rail after Japanese knotweed grew into their gardens from an adjoining railway, albeit without causing any damage to their properties.

In this case, the Court also ruled in favour of the claimants. They found knotweed was an actionable nuisance before it caused physical damage on neighbouring land because of the harmful effect on the land’s value. Network Rail is appealing this decision.

Conclusions

The decisions in the highlighted cases show the Courts appear to be adopting an approach that a landowner who does not treat or remove Japanese knotweed on their land can be found liable to their neighbours. 

Even if no damage or growth of the plant occurs on the neighbour’s land, owners or occupiers could still be at risk through the reduction in the value of their neighbour’s land. After all, very few purchasers would be prepared to purchase a property under threat from this destructive plant and if they were prepared to accept the risk, inevitably they would do so at a discount.

These cases could also lead to a number of similar other claims being pursued and it will be interesting to see the Court’s decision in the Network Rail case on appeal.


Chris Langford is a Trainee Solicitor within Berwins' commercial litigation team. 

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